Re: [RFC PATCH 01/56] Documentation/admin-guide: Add documentation

Josh Poimboeuf
2025-10-16T21:24:55Z

On Mon, Oct 13, 2025 at 09:33:49AM -0500, David Kaplan wrote:
> +Runtime Limitations
> +^^^^^^^^^^^^^^^^^^^
> +
> +There are a few mitigations that cannot be toggled at runtime due to the way
> +they are structured. Specifically, kernel PTI (page table isolation) cannot be
> +toggled because of the complexity of this mitigation. Additionally, SMT cannot
> +be disabled at runtime. Therefore, if a bug mitigation requires disabling SMT,
> +a warning message will be printed.

Is there a particular reason SMT can't be disabled? There's definitely
a way to do it, see /sys/devices/system/cpu/smt/{active,control}.

--
Josh